Large animals such as sika deer are considered to have diverse impacts on the aboveground and belowground processes in terrestrial ecosystems. Previous studies on the ecological impacts of deer grazing have been mostly conducted in open ecosystems where the home ranges of the deer are not restricted; however, few studies have been conducted in closed ecosystems. The present study was carried out to investigate the impact of deer on soils and plants in Nakajima Island in Lake Toya, where sika deer populations are dense within the closed ecosystem. We used six deer fences on the island and examined the physical and chemical properties of soils along with the chemical properties of plants. The thickness of litter layer on the soil surface was smaller and the surface soil hardness was larger outside the fences than inside. In addition, the soil nitrogen characteristics inside and outside the fence varied with the locations, especially the grassland soil outside the fence had higher nitrate-N than the forests. Similarly, nitrogen concentrations in Japanese spurge leaves were significantly higher outside the fences in the grassland than inside. These results suggest that in Nakajima Island, increased density of deer variously changes the physical properties of the soils and the chemical properties of the soils and plants, and these changes vary based on deer abundance and vegetation type. Because ranges for the movement of deer are limited in Nakajima Island, the effects of high deer density could be observed over the island, and stabilized for long time.
Air dose rate is an important indicator that shows spatial distributions of radionuclides contaminations derived from Fukushima Daiichi nuclear power plant accident, however, studies which analyzed spatial and temporal patterns of air dose rates in forests in 2011, the initial stage of environmental radioactivity, were scarce. The spatial distributions and the temporal changes of the air dose rates among three types of forest stands (seed orchards, Japanese red pine and deciduous hardwood forests, Japanese cedar forests) at the height of 0.1 m and 1.0 m above the ground from June to November, 2011 in Koriyama city, Fukushima Prefecture, were investigated. In June 2011, the air dose rates were associated with the vegetation types (seed orchards > Japanese red pine and deciduous hardwood forest > Japanese cedar forest). It was suggested that the air dose rates influenced by canopy interceptions during the initial atmospheric fallout. The time-depended changes of air dose rates varied among three types of the forests from June to November, 2011, decrease rates of air dose were in the order of seed orchards, the Japanese red pine and deciduous hardwood forests and the Japanese cedar forests. Therefore, it was suggested that the time-depended changes of air dose rates were influenced by vertical migration processes of radionuclides such as above the ground and below the ground.
Knowledge about carbon dynamics on the organic matter pooled in the forest soil was important as basic data to discuss the effect of the progress of global warming. In this study, one treatment area (0.23 ha) and one control area (0.24 ha) were set in a 35-year-old Cryptomeria japonica plantation of Tokyo University of Agriculture Okutama Forest in Okutama-machi, Nishitama-gun, Tokyo, in December 2012, and clear-cutting and ground clearance were done in the treatment area in March 2013. Fixed-point measurements of soil respiration rate (RS) were conducted regularly from January 2013 to December 2018 at 19 and 21 points in the treatment and the control areas, respectively. Volcanic ash soil distributes in the study site. From the comparison of RS estimated at 20℃ （RS20), the ratios of RS20 in the treatment area to the control area were increasing from 0.60 in 2013 to 0.74 (highest) in 2016, but decreased to 0.49 in 2018. The carbon stocks in the surface soil (0-5 cm deep) measured in 2018 were 24.6 t ha-1 at the treatment area and 23.2 t ha-1 at the control area. The total carbon emission for six years was estimated to be 50.3 tC ha-1 in the treatment area, which could not be explained by the decomposition of the organic matter pooled in the surface soil before harvesting. These results support the importance of the carbon pool of subsurface soil for consideration of soil carbon dynamics.
Picea glehnii is a key forestry species in Hokkaido, Japan. Here we evaluated the variation in probable occurrence of basal and stem bending among sites with different climatic conditions and among maternal families. Common families were planted at 9 test sites and basal and stem bending degrees were observed at the age of 20 years (five-level ordered categorical data). Data were analyzed using an ordered logit model, and the effect of sites, blocks within site, plots within site, families and the interaction between site and family were evaluated. Relatively high levels of site, block and plot effects were observed, and strong negative and positive effects were observed in the sites within northern Hokkaido and within central Hokkaido, respectively. In addition, plots which showed significant positive and negative effect were concentrated in each site. These results indicated that environmental conditions such as snowfall, as well as local topography have considerable effect on basal and stem bending. The effect of families on basal and stem bending was low compare to the environmental factors, but some families exhibited significant positive or negative effects. On the other hand, no interaction between site and family was detected. Therefore, genetically superior families exist regardless of the environmental conditions, and resistance to basal and stem bending thought to be improved by breeding in P. glehnii.
Forestation in drylands has been progressing to prevent desertification and mitigate climate change. Aiming to improve the water holding capacity of soils and increase survival and growth of tree seedlings, superabsorbent polymers (SAP) are sometimes used in dry and semi-dry climates. We reviewed the basic knowledge of the physical, chemical, and biological properties of soils amended with SAP. We also discussed the effective usage of SAP in forestation. Soils amended by SAP have the following characteristics: 1) increased water holding capacity, which is evident in sandy soils rather than clayey soils; 2) soil water potential in SAP-amended soils mostly applies to water below pF 2.5 (readily available water), and to a lesser extent to water over pF 4.2 (unavailable water); 3) water retention and absorption curves show a hysteresis, indicating that a greater volume of water is held during the desorption process; 4) SAP application is not effective in high salinity water; 5) the large size of SAP improves pore characteristics of heavy-clay soils by creating coarse pores in the soil; 6) SAP expansion by water absorption decreases water permeability in the soil; 7) cation exchangeable capacity (CEC) of soil increases by SAP application; 8) soil microbial biomass increases due to the soil moistening by SAP; 9) no harmful effect on the environmental contamination is detected after SAP application. We recommend limiting the effective use of SAP to sandy or stony soils with coarse pores and soil with relatively low salinity in drylands. Further study is needed to develop the combined use of fertilizers and SAP in order to improve the quality of degraded infertile soils.